- Finding Feature Information
- Weighted Random Early Detection Configuration Task List
- DWRED Configuration Task List
- Flow-Based WRED Configuration Task List
- DiffServ Compliant WRED Configuration Task List
- WRED Configuration Examples
- DWRED Configuration Examples
- Flow-Based WRED Configuration Example
- DiffServ Compliant WRED Configuration Examples
Configuring Weighted Random Early Detection
Feature History
| Release |
Modification |
|---|---|
| Cisco IOS |
For information about feature support in Cisco IOS software, use Cisco Feature Navigator. |
This module describes the tasks for configuring Weighted Random Early Detection (WRED), distributed WRED (DWRED), flow-based WRED, and DiffServ Compliant WRED on a router.
 Note |
WRED is useful with adaptive traffic such as TCP/IP. With TCP, dropped packets indicate congestion, so the packet source will reduce its transmission rate. With other protocols, packet sources may not respond or may resend dropped packets at the same rate. Thus, dropping packets does not decrease congestion. WRED treats non-IP traffic as precedence 0, the lowest precedence. Therefore, non-IP traffic is more likely to be dropped than IP traffic. You cannot configure WRED on the same interface as Route Switch Processor (RSP)-based custom queueing (CQ), priority queueing (PQ), or weighted fair queueing (WFQ). However, you can configure both DWRED and DWFQ on the same interface. |
Random Early Detection (RED) is a congestion avoidance mechanism that takes advantage of the congestion control mechanism of TCP. By randomly dropping packets prior to periods of high congestion, RED tells the packet source to decrease its transmission rate. WRED drops packets selectively based on IP precedence. Edge routers assign IP precedences to packets as they enter the network. (WRED is useful on any output interface where you expect to have congestion. However, WRED is usually used in the core routers of a network, rather than at the edge.) WRED uses these precedences to determine how it treats different types of traffic.
When a packet arrives, the following events occur:
- The average queue size is calculated.
- If the average is less than the minimum queue threshold, the arriving packet is queued.
- If the average is between the minimum queue threshold for that type of traffic and the maximum threshold for the interface, the packet is either dropped or queued, depending on the packet drop probability for that type of traffic.
- If the average queue size is greater than the maximum threshold, the packet is dropped.
- Finding Feature Information
- Weighted Random Early Detection Configuration Task List
- DWRED Configuration Task List
- Flow-Based WRED Configuration Task List
- DiffServ Compliant WRED Configuration Task List
- WRED Configuration Examples
- DWRED Configuration Examples
- Flow-Based WRED Configuration Example
- DiffServ Compliant WRED Configuration Examples
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Weighted Random Early Detection Configuration Task List
Enabling WRED
Note |
To avoid counter issues do not configure WRED and queue-limit on the same interface at the same time. |
| Command |
Purpose |
|---|---|
Router(config-if)# random-detect |
Enables WRED. If you configure this command on a Versatile Interface Processor (VIP) interface, DWRED is enabled. |
Changing WRED Parameters
Note |
The default WRED parameter values are based on the best available data. We recommend that you do not change the parameters from their default values unless you have determined that your applications will benefit from the changed values. |
| Command |
Purpose |
|---|---|
Router(config-if)# random-detect exponential-weighting-constant exponent |
Configures the weight factor used in calculating the average queue length. |
Router(config-if)# random-detect precedence precedence min-threshold max-threshold mark-prob-denominator |
Configures parameters for packets with a specific IP Precedence. The minimum threshold for IP Precedence 0 corresponds to half the maximum threshold for the interface. Repeat this command for each precedence. To configure RED, rather than WRED, use the same parameters for each precedence. |
Monitoring WRED
| Command |
Purpose |
|---|---|
Router# show queue interface-type interface-number |
Displays the header information of the packets inside a queue. This command does not support DWRED. |
Router# show queueing interface interface-number [vc [[vpi /] vci]] |
Displays the WRED statistics of a specific virtual circuit (VC) on an interface. |
Router# show queueing random-detect |
Displays the queueing configuration for WRED. |
Router# show interfaces [type slot | port-adapter | port] |
Displays WRED configuration on an interface. |
DWRED Configuration Task List
- Configuring DWRED in a Traffic Policy
- Configuring DWRED to Use IP Precedence Values in a Traffic Policy
- Monitoring and Maintaining DWRED
Configuring DWRED in a Traffic Policy
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
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Specifies the name of the traffic policy to be created or modified. |
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Specifies the name of a traffic class to be created and included in the traffic policy |
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Configures the exponential weight factor used in calculating the average queue length. |
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Specifies the amount of bandwidth, in kbps, to be assigned to the traffic class. |
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Specifies the number of queues to be reserved for the traffic class. |
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Specifies the maximum number of packets that can be queued for the specified traffic class. |
Configuring DWRED to Use IP Precedence Values in a Traffic Policy
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
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Specifies the name of the traffic policy to be created or modified. |
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Specifies the name of a traffic class to associate with the traffic policy |
|
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Configures the exponential weight factor used in calculating the average queue length. |
|
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Configures the parameters for packets with a specific IP Precedence. The minimum threshold for IP Precedence 0 corresponds to half the maximum threshold for the interface. Repeat this command for each precedence. |
Monitoring and Maintaining DWRED
| Command |
Purpose |
|---|---|
Router#
show policy-map |
Displays all configured traffic policies. |
Router# show policy-map policy-map-name |
Displays the user-specified traffic policy. |
Router#
show policy-map interface |
Displays statistics and configurations of all input and output policies attached to an interface. |
Router# show policy-map interface interface-spec |
Displays configuration and statistics of the input and output policies attached to a particular interface. |
Router# show policy-map interface interface-spec input |
Displays configuration and statistics of the input policy attached to an interface. |
Router# show policy-map interface interface-spec output |
Displays configuration statistics of the output policy attached to an interface. |
Router# show policy-map interface [interface-spec [input | output] [class class-name]]]] |
Displays the configuration and statistics for the class name configured in the policy. |
Flow-Based WRED Configuration Task List
Configuring Flow-Based WRED
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
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Enables flow-based WRED. |
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Sets the flow threshold multiplier for flow-based WRED. |
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Sets the maximum flow count for flow-based WRED. |
DiffServ Compliant WRED Configuration Task List
- Configuring WRED to Use the Differentiated Services Code Point Value
- Verifying the DSCP Value Configuration
Configuring WRED to Use the Differentiated Services Code Point Value
WRED at the Interface Level
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
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Indicates that WRED is to use the DSCP value when it calculates the drop probability for the packet. |
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Specifies the minimum and maximum thresholds, and, optionally, the mark-probability denominator for the specified DSCP value. |
WRED at the per-VC Level
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
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Indicates that WRED is to use the DSCP value when it calculates the drop probability for the packet. |
|
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Specifies the DSCP value, the minimum and maximum packet thresholds and, optionally, the mark-probability denominator for the DSCP value. |
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Enables per-VC WRED or per-VC VIP-DWRED. |
WRED at the Class Level
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
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Creates a class map to be used for matching packets to a specified class. |
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Configures the match criteria for a class map. |
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Creates or modifies a policy map that can be attached to one or more interfaces to specify a traffic policy. |
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Specifies the QoS actions for the default class. |
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Specifies or modifies the bandwidth allocated for a class belonging to a policy map. |
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Indicates that WRED is to use the DSCP value when it calculates the drop probability for the packet. |
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Specifies the minimum and maximum packet thresholds and, optionally, the mark-probability denominator for the DSCP value. |
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Attaches a policy map to an output interface or VC to be used as the traffic policy for that interface or VC. |
Verifying the DSCP Value Configuration
| Command |
Purpose |
|---|---|
Router# show queueing interface |
Displays the queueing statistics of an interface or VC. |
Router# show policy-map interface |
Displays the configuration of classes configured for traffic policies on the specified interface or permanent virtual circuit (PVC). |
WRED Configuration Examples
Example WRED Configuration
The following example enables WRED with default parameter values:
interface Serial5/0 description to qos1-75a ip address 200.200.14.250 255.255.255.252 random-detect
Use the show interfaces command output to verify the configuration. Notice that the "Queueing strategy" report lists "random early detection (RED)."
Router# show interfaces serial 5/0
Serial5/0 is up, line protocol is up
Hardware is M4T
Description: to qos1-75a
Internet address is 200.200.14.250/30
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 237/255
Encapsulation HDLC, crc 16, loopback not set
Keepalive not set
Last input 00:00:15, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:05:08
Input queue: 0/75/0 (size/max/drops); Total output drops: 1036
Queueing strategy: random early detection(RED)
5 minutes input rate 0 bits/sec, 2 packets/sec
5 minutes output rate 119000 bits/sec, 126 packets/sec
594 packets input, 37115 bytes, 0 no buffer
Received 5 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
37525 packets output, 4428684 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up
Use the show queue command output to view the current contents of the interface queue. Notice that there is only a single queue into which packets from all IP precedences are placed after dropping has taken place. The output has been truncated to show only three of the five packets.
Router# show queue serial 5/0
Output queue for Serial5/0 is 5/0
Packet 1, linktype: ip, length: 118, flags: 0x288
source: 190.1.3.4, destination: 190.1.2.2, id: 0x0001, ttl: 254,
TOS: 128 prot: 17, source port 11111, destination port 22222
data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x4321
0x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765
Packet 2, linktype: ip, length: 118, flags: 0x288
source: 190.1.3.5, destination: 190.1.2.2, id: 0x0001, ttl: 254,
TOS: 160 prot: 17, source port 11111, destination port 22222
data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x4321
0x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765
Packet 3, linktype: ip, length: 118, flags: 0x280
source: 190.1.3.6, destination: 190.1.2.2, id: 0x0001, ttl: 254,
TOS: 192 prot: 17, source port 11111, destination port 22222
data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x4321
0x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765
Use the show queueing command output to view the current settings for each of the precedences. Also notice that the default minimum thresholds are spaced evenly between half and the entire maximum threshold. Thresholds are specified in terms of packet count.
Router# show queueing
Current random-detect configuration:
Serial5/0
Queueing strategy:random early detection (WRED)
Exp-weight-constant:9 (1/512)
Mean queue depth:28
Class Random Tail Minimum Maximum Mark
drop drop threshold threshold probability
0 330 0 20 40 1/10
1 267 0 22 40 1/10
2 217 0 24 40 1/10
3 156 0 26 40 1/10
4 61 0 28 40 1/10
5 6 0 31 40 1/10
6 0 0 33 40 1/10
7 0 0 35 40 1/10
rsvp 0 0 37 40 1/10
Example Parameter-Setting DWRED
The following example specifies the same parameters for each IP precedence. Thus, all IP precedences receive the same treatment. Start by enabling DWRED.
interface FastEthernet1/0/0 ip address 200.200.14.250 255.255.255.252 random-detect
Next, enter the show queueing random-detect command to determine reasonable values to use for the precedence-specific parameters.
Router# show queueing random-detect
Current random-detect configuration:
FastEthernet2/0/0
Queueing strategy:fifo
Packet drop strategy:VIP-based random early detection (DWRED)
Exp-weight-constant:9 (1/512)
Mean queue depth:0
Queue size:0 Maximum available buffers:6308
Output packets:5 WRED drops:0 No buffer:0
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 109 218 1/10 5
1 0 0 122 218 1/10 0
2 0 0 135 218 1/10 0
3 0 0 148 218 1/10 0
4 0 0 161 218 1/10 0
5 0 0 174 218 1/10 0
6 0 0 187 218 1/10 0
7 0 0 200 218 1/10 0
Complete the configuration by assigning the same parameter values to each precedence. Use the values obtained from the show queueing random-detect command output to choose reasonable parameter values.
interface FastEthernet1/0/0 random-detect precedence 0 100 218 10 random-detect precedence 1 100 218 10 random-detect precedence 2 100 218 10 random-detect precedence 3 100 218 10 random-detect precedence 4 100 218 10 random-detect precedence 5 100 218 10 random-detect precedence 6 100 218 10 random-detect precedence 7 100 218 10
Example Parameter-Setting WRED
The following example enables WRED on the interface and specifies parameters for the different IP precedences:
interface Hssi0/0/0 description 45Mbps to R1 ip address 10.200.14.250 255.255.255.252 random-detect random-detect precedence 0 32 256 100 random-detect precedence 1 64 256 100 random-detect precedence 2 96 256 100 random-detect precedence 3 120 256 100 random-detect precedence 4 140 256 100 random-detect precedence 5 170 256 100 random-detect precedence 6 290 256 100 random-detect precedence 7 210 256 100 random-detect precedence rsvp 230 256 100
DWRED Configuration Examples
Example DWRED on an Interface
The following example configures DWRED on an interface with a weight factor of 10:
Router(config)# interface hssi0/0/0 Router(config-if)# description 45mbps to R1 Router(config-if)# ip address 192.168.14.250 255.255.255.252 Router(config-if)# random-detect Router(config-if)# random-detect exponential-weighting-constant 10
Example Modular QoS CLI
The following example enables DWRED using the Legacy CLI (non-Modular QoS Command-Line Interface) feature on the interface and specifies parameters for the different IP precedences:
interface Hssi0/0/0 description 45Mbps to R1 ip address 200.200.14.250 255.255.255.252 random-detect random-detect precedence 0 32 256 100 random-detect precedence 1 64 256 100 random-detect precedence 2 96 256 100 random-detect precedence 3 120 256 100 random-detect precedence 4 140 256 100 random-detect precedence 5 170 256 100 random-detect precedence 6 290 256 100 random-detect precedence 7 210 256 100 random-detect precedence rsvp 230 256 100
The following example uses the Modular QoS CLI to configure a traffic policy called policy10. For congestion avoidance, WRED packet drop is used, not tail drop. IP Precedence is reset for levels 0 through 5.
policy-map policy10 class acl10 bandwidth 2000 random-detect exponential-weighting-constant 10 random-detect precedence 0 32 256 100 random-detect precedence 1 64 256 100 random-detect precedence 2 96 256 100 random-detect precedence 3 120 256 100 random-detect precedence 4 140 256 100 random-detect precedence 5 170 256 100
Example Configuring DWRED in Traffic Policy
The following example configures policy for a traffic class named int10 to configure the exponential weight factor as 12. This is the weight factor used for the average queue size calculation for the queue for traffic class int10. WRED packet drop is used for congestion avoidance for traffic class int10, not tail drop.
policy-map policy12 class int10 bandwidth 2000 random-detect exponential-weighting-constant 12
Flow-Based WRED Configuration Example
The following example enables WRED on the serial interface 1 and configures flow-based WRED. The random-detect interface configuration command is used to enable WRED. Once WRED is enabled, the random-detect flow command is used to enable flow-based WRED.
After flow-based WRED is enabled, the random-detect flow average-depth-factor command is used to set the scaling factor to 8 and the random-detect flow count command is used to set the flow count to 16. The scaling factor is used to scale the number of buffers available per flow and to determine the number of packets allowed in the output queue for each active flow.
configure terminal interface Serial1 random-detect random-detect flow random-detect flow average-depth-factor 8 random-detect flow count 16 end
The following part of the example shows a sample configuration file after the previous flow-based WRED commands are issued:
Router# more system:running-config
Building configuration...
Current configuration:
!
version 12.0
service timestamps debug datetime msec localtime
service timestamps log uptime
no service password-encryption
service tcp-small-servers
!
no logging console
enable password lab
!
clock timezone PST -8
clock summer-time PDT recurring
ip subnet-zero
no ip domain-lookup
!
interface Ethernet0
no ip address
no ip directed-broadcast
no ip mroute-cache
shutdown
!
interface Serial0
no ip address
no ip directed-broadcast
no ip mroute-cache
no keepalive
shutdown
!
interface Serial1
ip address 190.1.2.1 255.255.255.0
no ip directed-broadcast
load-interval 30
no keepalive
random-detect
random-detect flow
random-detect flow count 16
random-detect flow average-depth-factor 8
!
router igrp 8
network 190.1.0.0
!
ip classless
no ip http server
!
line con 0
transport input none
line 1 16
transport input all
line aux 0
transport input all
line vty 0 4
password lab
login
!
end
DiffServ Compliant WRED Configuration Examples
Example WRED Configured to Use the DSCP Value
The following example configures WRED to use the DSCP value 8. The minimum threshold for the DSCP value 8 is 24 and the maximum threshold is 40. This configuration was performed at the interface level.
Router(config-if)# interface seo/0 Router(config-if)# random-detect dscp-based Router(config-if)# random-detect dscp 8 24 40
The following example enables WRED to use the DSCP value 9. The minimum threshold for the DSCP value 9 is 20 and the maximum threshold is 50. This configuration can be attached to other VCs, as required.
Router(config)# random-detect-group sanjose dscp-based Router(cfg-red-grp)# dscp 9 20 50 Router(config-subif-vc)# random-detect attach sanjose
The following example enables WRED to use the DSCP value 8 for the class c1. The minimum threshold for the DSCP value 8 is 24 and the maximum threshold is 40. The last line attaches the traffic policy to the output interface or VC p1.
Router(config-if)# class-map c1 Router(config-cmap)# match access-group 101 Router(config-if)# policy-map p1 Router(config-pmap)# class c1 Router(config-pmap-c)# bandwidth 48 Router(config-pmap-c)# random-detect dscp-based Router(config-pmap-c)# random-detect dscp 8 24 40 Router(config-if)# service-policy output p1
Example DSCP Value Configuration Verification
When WRED has been configured to use the DSCP value when it calculates the drop probability of a packet, all entries of the DSCP table are initialized with the appropriate default values. The example in the following section are samples of the show policy interface command for WRED at the class level.
This example displays packet statistics along with the entries of the DSCP table, confirming that WRED has been enabled to use the DSCP value when it calculates the drop probability for a packet.
Router# show policy interface Serial6/3
Serial6/3
Service-policy output: test
Class-map: c1 (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol ip
0 packets, 0 bytes
5 minute rate 0 bps
Weighted Fair Queueing
Output Queue: Conversation 265
Bandwidth 20 (%)
Bandwidth 308 (kbps)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
exponential weight: 9
mean queue depth: 0
dscp Transmitted Random drop Tail drop Minimum Maximum Mark
pkts/bytes pkts/bytes pkts/bytes thresh thresh prob
af11 0/0 0/0 0/0 32 40 1/10
af12 0/0 0/0 0/0 28 40 1/10
af13 0/0 0/0 0/0 24 40 1/10
af21 0/0 0/0 0/0 32 40 1/10
af22 0/0 0/0 0/0 28 40 1/10
af23 0/0 0/0 0/0 24 40 1/10
af31 0/0 0/0 0/0 32 40 1/10
af32 0/0 0/0 0/0 28 40 1/10
af33 0/0 0/0 0/0 24 40 1/10
af41 0/0 0/0 0/0 32 40 1/10
af42 0/0 0/0 0/0 28 40 1/10
af43 0/0 0/0 0/0 24 40 1/10
cs1 0/0 0/0 0/0 22 40 1/10
cs2 0/0 0/0 0/0 24 40 1/10
cs3 0/0 0/0 0/0 26 40 1/10
cs4 0/0 0/0 0/0 28 40 1/10
cs5 0/0 0/0 0/0 30 40 1/10
cs6 0/0 0/0 0/0 32 40 1/10
cs7 0/0 0/0 0/0 34 40 1/10
ef 0/0 0/0 0/0 36 40 1/10
rsvp 0/0 0/0 0/0 36 40 1/10
default 0/0 0/0 0/0 20 40 1/10
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